192 



DESMIDIACE&. 



PART II. 



the nature of their component materials is by chemical 

 tests. A solution of iodine turns starch blue, and cel- 

 lulose brown, and thus it is found that the interior of the 

 Desmidiacese is occupied by a mass of starch granules, 

 covered with chlorophyll, and mixed with a formative 

 fluid. This mass, enclosed in a delicate membrane, consti- 

 tutes the primordial cell; it has an exterior coat of firm 

 cellulose, and the whole is more or less enveloped in a 

 gelatinous substance. Like other plants, when, in bright 



Fig. 9. Various species of Staurastrum: A, vestitum; B, aculeatum; c, paradoxum ; 

 D, K, brachiatum. 



sunshine, the Desmidiacese decompose carbonic acid 

 gas, give off the oxygen, and assimilate the carbon into 

 chlorophyll. 



These plants are frequently distinguished by projec- 

 tions from their cellulose coat above their surface, 

 these being sometimes short and conspicuous, but often 

 projected in spines, which form a beautiful symmetrical 

 hyaline border round the green internal cell, as shown 

 in fig. 9. Another peculiarity of the Desmidiacese is the 

 appearance of their being divided into two symmetrical 

 parts by a satural line, as the name implies, though 

 there is no real division. 



